1. Field of the Invention
This invention generally relates to the manufacture of soft contact lenses using a polymerizable monomer or monomer mixture. More specifically, the invention relates to methods and apparatus for moving lens carriers in such a manufacturing process. Even more specifically, the invention relates to such methods and apparatus that are particularly well suited for moving the lens carriers through pre-curing and curing stations.
2. Prior Art
Over the last several years, systems have been successfully developed for the automated, mass production of soft contact lenses using a direct molding process. One such system is disclosed in U.S. Pat. No. 6,220,845, the entire disclosure of which is hereby incorporated herein in its entirety by reference.
Generally, in the system disclosed in U.S. Pat. No. 6,220,845, each lens is formed by sandwiching a monomer between back and front mold halves. The monomer is polymerized, thus forming a lens that is then removed from the mold halves, further treated, and packaged for consumer use. In order to polymerize the monomer, it has been found advantageous to pass the monomer through both a pre-cure and a curing step.
In the pre-cure step, the mold halves are held together under pressure while the polymerization is begun. Typically, the monomer composition includes initiators that work upon exposure to ultraviolet or visible radiation; and, in the pre-cure step, while the mold halves are held together, the composition is exposed to such radiation of an intensity and duration effective to initiate polymerization. After the pre-cure step, the monomer is again exposed to ultraviolet or visible radiation in a cure step in which the polymerization is permitted to proceed to completion.
More than one lens can be cured at a time, and the throughput of the lens manufacturing process can be increased by increasing the number of lenses being cured at the same time. Simply increasing the number of lenses being cured at one time is complicated, however, by several factors. For example, as this number increases, the size of the area or areas needed for the pre-cure and curing also tends to increase, and other design constraints or considerations may limit the size of this area or areas. In addition, as the number of lenses that are in the pre-cure and cure areas increases, the design and operation of the article handling apparatus used to move all of these lenses into, through, and out of these areas may become excessively complicated.